The Internet, like so many other high tech developments, grew from research originally performed by the United States Department of Defense. In the 1960s, the military had accumulated a large collection of incompatible computer networks. Because of their incompatible data structures and transmission protocols, many of these computers could not communicate with other computers across network boundaries.
In the 1960s, the Defense Department wanted to develop a communication system that would permit communication between these different computer networks. Recognizing that a single, centralized communication system would be vulnerable to attacks or sabotage, the Defense Department required that the communication system be decentralized with no critical services concentrated in vulnerable failure points. In order to achieve this goal, the Defense Department established a decentralized communication protocol for communication between the computer networks.
A few years later, the National Science Foundation (NSF) wanted to facilitate communication between incompatible network computers at various research institutions across the country. The NSF adopted the Defense Department's protocol for communication, and this combination of research computer networks would eventually evolve into the Internet.
Internet Protocols
The Defense Department's communication protocol governing data transmission between different networks was called the Internet Protocol (IP) standard. The IP standard has been widely adopted for the transmission of discrete information packets across network boundaries. In fact, the IP standard is the standard protocol governing communications between computers and networks on the Internet.
The IP standard identifies the types of services to be provided to users and specifies the mechanisms needed to support these services. The IP standard also specifies the upper and lower system interfaces, defines the services to be provided on these interfaces, and outlines the execution environment for services needed in the system.
Two types of transmission protocols may operate with the IP protocol—the Transmission Control Protocol (TCP) or the User Datagram Protocol (UDP). TCP was developed to provide connection-oriented, end-to-end data transmission between packet-switched computer networks, and UDP supports a connection-less transmission between computer networks. Unlike UDP, TCP provides certain error recovery and data-checking services. The combination of TCP or UDP with the IP protocol forms a suite of protocols for communication between computers on the Internet and has become a standard protocol for use in all packet switching networks that provide connectivity across network boundaries.
In a typical Internet-based communication scenario, data is transmitted from an originating communication device on a first network across a transmission medium to a destination communication device on a second network. After receipt at the second network, the network routes the packet to a destination communication device. Because Internet communication uses standard protocols, the IP protocol on the destination communication device decodes the transmitted information into the original information transmitted by the originating device.
TCP/IP Addressing and Routine
A computer operating on a network is assigned a unique physical address under the TCP/IP protocols. This is called an IP address. The IP address can include: (1) a network ID and number identifying a network, (2) a sub-network ID number identifying a substructure on the network, and (3) a host ID number identifying a particular computer on the sub-network. A header data field in the information packet will include source and destination addresses. The IP addressing scheme imposes a consistent addressing scheme that reflects the internal organization of the network or sub-network.
A router is used to regulate the transmission of information packets into and out of the computer network. Routers interpret the logical address contained in information packet headers and direct the information packets to the intended destination. Information packets addressed between computers on the same network do not pass through a router on the boundary of the network, and as such, these information packets will not clutter the transmission lines outside the network. If data is addressed to a computer outside the network, the router on the network boundary forwards the data onto the greater network.
TCP/IP network protocols define how routers determine the transmission path through a network and across network boundaries. Routing decisions are based upon information in the IP header and corresponding entries in a routing table maintained on the router. A routing table contains the information for a router to determine whether to accept an information packet on behalf of a device or pass the information packet onto another router.
Routing tables can be configured manually with routing table entries or with a dynamic routing protocol. A manual routing table can be configured upon initialization. In a dynamic routing protocol, routers update routing information with periodic information packet transmissions to other routers on the network. The dynamic routing protocol accommodates changing network topologies, network architecture, network structure, layout of routers, and interconnection between hosts and routers.
The IP-Based Mobility System
The Internet protocols were originally developed with an assumption that Internet users would be statically connected to a fixed network. With the advent of cellular wireless communication systems, such as mobile communication devices, the movement of Internet users within a network and across network boundaries has become common. Because of this highly mobile Internet usage, the implicit design assumption of the Internet protocols (e.g. a fixed or static user location) is violated by the mobility of the user.
In an IP-based mobile communication system, the mobile communication device (e.g. cellular phone, pager, computer, etc.) can be called a mobile node. Typically, a mobile node maintains connectivity to its home network through a foreign network. The mobile node will always be associated with its home network for IP addressing purposes, and the mobile node will have information routed to it by routers located on the home and foreign networks. The routers can be referred to by a number of names including Home Agent, Home Mobility Manager, Home Location Register, Foreign Agent, Serving Mobility Manager, Visited Location Register, and Visiting Serving Entity.
While coupled to a foreign network, the mobile node is assigned a care-of address. This care-of address is a temporary IP address assigned by the foreign network. Routers on the home and foreign network use the care-of address to route information packets addressed to the mobile node while it resides on the foreign network. During mobile IP communication, the mobile node obtains the care-of address while establishing a wireless link with the foreign agent. The mobile node then transmits a registration message containing the care-of address to the home agent, which updates a routing table entry for the mobile node with the care-of address. When the home network receives information packets addressed to the mobile node, the home agent appends the care-of address to the packet's address header. The modified packets are then forwarded to the correct location using the appended care-of address.
While residing on a foreign network, a mobile node may move from one location to another, changing its connectivity on the foreign network. This movement changes the physical location of the mobile node and requires updating routing tables and care-of addressing to keep up with the movement of the mobile node. Each time the mobile node changes its physical connection to the network, a new registration message is transmitted to the home agent to update the associated routing table entry and permit forwarding of the information packets to the correct location as specified by the care-of address.
Heterogeneous Networks
Many different types of wireless Internet systems are expected to be developed in the future. For instance, heterogeneous networks are envisioned with integrated Third Generation Partnership Project (3GPP) based systems (e.g. Generalized Packet Radio Service (GPRS) derivative systems), Third Generation Partnership Project 2 (3PGPP2) based systems (e.g. IS-95 and Code Division Multiple Access (CDMA) derivative systems), Universal Mobile Telecommunication System (UMTS) based systems, and Wireless Land Access Network (WLAN) based systems. Each network will provide different speeds and levels of coverage as required for optimal communication and utilization of resources for particular uses and users.
Communication devices and subsystems will be expected to automatically select and utilize the appropriate communication system format for a given communication service or utilization. For example, a mobile device may automatically select and utilize a WLAN while indoors, switching to cellular communications when it moves outdoors. This type of service selection and switching will optimize communication services and performance.
Authenticate, Authorize and Accounting (“AAA”)
When a mobile node is operating on a foreign network, specialized servers are used to authenticate, authorize, and collect accounting information for services rendered to the mobile node. This authentication, authorization, and accounting activity is called “AAA,” and AAA computer servers on the home and foreign network perform many of the required functions for AAA activities.
Authentication is the process of proving one's claimed identity, and security systems on a mobile IP network will often require authentication of the system user's identity before authorizing a requested activity. The AAA server authenticates the identity of an authorized user and authorizes the mobile node's requested activity. Additionally, the AAA server performs the accounting functions by tracking usage on the network.
In a typical mobile communication session, the mobile node generates and transmits an access request message after establishing a connection to the foreign agent. The foreign agent processes the access request, extracting information from the data fields. The foreign agent in turn generates and transmits an access request message to an AAA server on the foreign network containing the information required for AAA. The foreign AAA server forwards the message to the home AAA server, which processes the access request message, authenticating and confirming authorization for the identified mobile node. The home AAA server then transmits an access accept message back to the foreign agent, which processes and forwards the access accept message to the mobile node. The access accept message authorizes the mobile node to establish a communication session using the home agent. This message exchange completes the authentication and authorization process.
With the authorization and authentication complete, the mobile node completes registration of a care-of address with the home agent and proceeds with a communication session. During the communication session, AAA messages are generated and transmitted by the foreign AAA server to the home AAA server for accounting purposes. The home AAA server records the information in the messages to a data storage medium (e.g. tape, computer memory, data disk, etc).
Remote Authentication Dial In User Service (RADIUS) is one widely utilized protocol for AAA. The RADIUS protocol defines message formats and data required for AAA that can be used on virtually any packet-based communication system. Functionally, RADIUS can perform client-server operations, network security, authentication, and accounting using a standard information encoding under a UDP transmission protocol. RADIUS AAA server computers are widely deployed over wireless networks utilizing the RADIUS protocol to perform AAA functions.
As the Internet and mobile communications has continued to evolve, no one standard accounting mechanism has been developed. Mobile IP provides a method for transparent routing of Internet protocol data packets between heterogeneous networks, such as 3GPP, 3GPP2, or WLAN type networks. However, these networks lack a common or compatible accounting protocol or mechanism. Both 3GPP and 3GPP2 have defined but incompatible accounting mechanisms, while WLAN lacks a defined, industry standard. For example, 3GPP2 provides a RADIUS-based accounting scheme capturing data on the Packet Data Serving Node (PDSN), which is also applicable for WLAN access networks. On the other hand, 3GPP uses the Gateway General Packet Radio Service Serving Node (GGSN) to capture accounting data, which is not applicable in CDMA or WLAN systems.
Without a common accounting procedure, performing the AAA functions on a heterogeneous networks with IP is very difficult, if not practically impossible. A common accounting protocol and mechanism would greatly simplify accounting and enhance mobility communications across heterogeneous networks, further encouraging development of integrated heterogeneous networks and optimized wireless packet-based communication.